Hyper IgM Syndrome, X-linked (XHIM) – CD40L Deficiency
- Inheritance: X-Linked recessive
- Gene: CD40L
- Protein: CD40L
- Tests: CD40L Gene Sequencing, CD40 Ligand Protein by Flow
Key Clinical and Laboratory Features
- Common clinical features: Recurrent bacterial sinopulmonary infections, Pneumocytis jiroveci pneumonia (particularly in patients under age 5), chronic diarrhea (cryptosporidium is common and may lead to sclerosing cholangitis, liver cirrhosis and neuroendocrine malignancies in the abdomen), neutropenia
- Other clinical features: Autoimmunity including cytopenias, hypoparathyroidism, nephritis, and rheumatoid arthritis. Anemia due to chronic parvovirus B19 infection.
- Physical exam: Tonsils and lymph nodes are typically present. Lymphadenopathy and hepatosplenomegaly are common.
- Common laboratory features: No expression/function of CD40 ligand. Normal T-cell counts and B-cell counts. IgM levels are typically elevated but may be normal while IgG and IgA levels are very low.